JPH08136268A - Ring laser gyroscope - Google Patents

Abstract

PURPOSE: To provide a ring laser gyroscope with construction easy to manufacture. CONSTITUTION: A ring laser 15 is formed by circulating a laser light clockwise and counterclockwise through a polygonal closed optical path. A laser gyroscope thus obtained detects an input angular velocity utilizing the fact that a frequency difference is generated between the light 15A turned clockwise and the light 15B turned counterclockwise when the ring laser 15 is rotated. To limit the lateral mode of a laser oscillation to a TEMg00 , the shape of more than one reflection surfaces out of a plurality of mirrors 11, 12 and 13 is so arranged to cause a diffraction loss to a laser light of a higher order mode than the TEM00 , thereby suppressing the laser oscillation of a higher order mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ring laser gyro used by being mounted on an aircraft or the like.

[0002]

2. Description of the Related Art FIG. 4 shows the structure of a conventional ring laser gyro. In the example of FIG. 4, three mirrors 11, 12, 13 are used.
Is adhered to the glass block 10, and the glass block 10
The case where the ring laser 15 is formed by orbiting the laser beam in the thin tube 14 formed in 1 is shown, but the ring laser may be formed by using three or more mirrors. One of the three mirrors 11, 12, 13 is a concave mirror in this example, and the other mirror is a plane mirror.

Reference numeral 19 is a dither driving means, and 20 is a piezoelectric element for controlling the optical path length. Since these elements are not directly related to the present invention, description of the configuration and operation thereof will be omitted. 16A and 16B are anodes for laser oscillation, and 17 is a cathode for laser oscillation. For example, a He-Ne gas, which is a laser medium, is enclosed in the thin tube 14 and the anode 1
Laser oscillation occurs by applying a voltage between the 6A and 16B and the cathode 17, and the clockwise light 15A and the counterclockwise light 1
5B occurs. Here, clockwise light 15A and counterclockwise light 1
5B will be collectively referred to as a ring laser 15.

The laser light used as the ring laser 15 interferes with each other to measure the frequency difference.
It is necessary that the laser light be in the mode, especially in the TEM ₀₀ mode. For this reason, in the past, the diaphragm 14 was limited to a part of the thin tube 14.
A is provided, and the diaphragm 14A limits the transmission diameter of the light flux of the ring laser 15 to oscillate only the TEM ₀₀ mode. That is, TE, which is the basic mode
The M ₀₀ mode laser light is most concentrated in the central part of the laser beam, and the other higher order modes TEM ₁₀ ,
Laser light such as TEM ₂₀ has a spread around the laser beam. Therefore, by providing the diaphragm 14A, the diaphragm 1 can be used for the laser beams of the higher-order modes TEM ₁₀ and TEM _20.
4A gives diffraction loss, so higher-order modes TEM ₁₀ , T
Laser oscillation of EM ₂₀ can be suppressed. As a result, the mode of laser oscillation in the narrow tube 14 can be limited to TEM ₀₀ due to the presence of the diaphragm 14A, and a single-mode laser beam can be obtained.

[0005]

As described above, in the conventional ring laser gyro, in order to oscillate only in the TEM ₀₀ mode, a part of the thin tube 14 is narrowed down to form the diaphragm 14A. The structure in which the diaphragm 14A is provided in this way has the following drawbacks. (1) When the diaphragm 14A is not provided, the optical axis is determined by the center position of the concave mirror 11. In other words, the optical axis is determined in association with the center position of the concave mirror 11. However, in the conventional ring laser gyro, the portion of the diaphragm 14A is thin, and the laser light receives the most diffraction loss by the diaphragm 14A. Therefore, the optical axis must be in the centerline of the diaphragm. Therefore, contrary to the case where the diaphragm 14A does not exist,
The position of the concave mirror 11 must be adjusted so as to match the defined optical axis. At this time, if there is a shape error in the glass block 10, the mirror 1 is provided for each glass block.
The mounting positions of 1, 12, 13 are different. Further, in order to give a proper amount of diffraction loss to the laser light, the allowable range of the diameter of the diaphragm 14A is narrow. In other words, a slight change in the positional relationship between the optical axis and the diaphragm 14A is important. Therefore, the adjustment amount of the concave mirror 11 is extremely small, and as a result, the optical axis adjustment becomes difficult. (2) Further, when the glass block 10 is deformed by applying a force, the magnitude of the laser output is likely to change. That is, when the glass block 10 is deformed and the relative position between the diaphragm 14A and the optical axis is changed, the diffraction loss received by the laser light is changed, so that the magnitude of the laser output is easily changed. (3) Further, since holes of different diameters have to be processed in the glass block 10 to form the diaphragm 14A, it takes time to manufacture the glass block 10. Further, since the diameter of the diaphragm 14A is important in order to make the magnitude of the diffraction loss appropriate, high precision is required for its processing.

The conventional ring laser gyro has the following three drawbacks. An object of the present invention is to provide a ring laser gyro in which the optical axis adjustment is simple, the output hardly fluctuates, and the glass block is relatively easy to process.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the oscillation mode of laser light is set to TEM.
_In order to limit the number to ₀₀ , instead of providing a diaphragm, any one of a plurality of mirrors 10, 11 and 12 or two or more reflecting surfaces may be formed for a laser beam of a higher mode other than the TEM ₀₀ mode. The shape is selected to give diffraction loss.

In this embodiment, three mirrors 11, 12,
A case where the ring laser 15 is formed by using 13 is shown.
Also in this example, the mirror 11 is a concave mirror, and the concave mirror 1
For example, a seal-like reflection limiting means 18 is attached while leaving the central portion of the first reflection surface, and the reflection limiting means 18 reduces the reflectance of a portion distant from the center of the concave mirror 11 by a predetermined value or more, and laser light of a higher mode. It is configured to give diffraction loss to.

The diameter d of the hole 18A formed in the central portion of the reflection limiting means 18 is selected to be about 1.5 to 2 times the diameter of the laser beam 15. The reason will be described with reference to FIG.
FIG. 3 shows the light distribution intensity in the TEM ₀₀ mode and the TEM ₁₀ and TEM ₂₀ modes. In FIG. 3, the horizontal axis represents the diameter direction of the laser light. W represents the radius of the laser beam. The diameter d of the hole 18A of the reflection limiting means 18 is selected to be 1.5 to 2.0 times the beam diameter 2W. Beam diameter 2W
Indicates the length of the line connecting the positions of the levels which are 1 / e ² (e is the base of the natural logarithm) lower than the peak value in the TEM ₀₀ mode. By limiting the reflected 1.5-2.0 times the diameter of the diameter 2W beam, with little give diffraction loss to light the TEM ₀₀ mode, TEM ₁₀ mode, TEM ₂₀
Δ for laser light of higher modes
The diffraction loss corresponding to K ₁ and ΔK ₂ is given. In this way, by giving the diffraction losses ΔK ₁ and ΔK ₂ in the closed optical path, the laser oscillation of the higher order mode is suppressed and only the TEM ₀₀ mode which is the fundamental mode can be oscillated.

That is, the transverse mode of laser light is the fundamental mode
Is a TEM₀₀The spread of the mode (Gaussian beam)
The smallest and higher transverse modes (TEM_Ten, TEM₀₁, T
EM ₁₁, TEM₂₀...), the wider the spread becomes. Obedience
Basic mode TEM₀₀Without giving diffraction loss to
In addition, the shape that gives diffraction loss to light of higher modes
By limiting the shape (diameter) of the shooting surface, the basic mode T
EM₀₀It can be limited to only laser oscillation.

In the above embodiment, the reflection limiting means 18 for suppressing the oscillation of the laser light of the higher order mode is attached to the concave mirror 11, but other flat mirrors 12,
It may be affixed to either one or both of the thirteen. In practice, the reflection limiting means 18 may be attached to any one of the mirrors for forming the closed optical path. Further, in reality, in the concave mirror 11, it is required to reflect the laser light at the center 11A of the concave surface. Therefore, in order to predefine the position where the reflection limiting means 18 is attached, the concave mirror 11 is required.
It is a desirable embodiment to attach the reflection limiting means 18 to the above since it is easier to determine the attaching position.

In other words, it is difficult to predefine the reflection position because the plane mirror may reflect the laser light anywhere. Therefore, it is advantageous in manufacturing to attach the reflection limiting means 18 to the concave mirror 11 whose reflection position is predetermined. On the other hand, although the reflection limiting means 18 has been described above by using an example in which a seal for reducing the reflectance is used, the diameter of the reflecting surface is limited in advance to about 1.5 to 2.0 times the beam diameter of the laser light. You may form it. Further, the reflection limiting means 18 may be drawn with paint or the like.

[0013]

As described above, according to the present invention, the oscillation mode of the laser light is reflected on the reflecting surface of the mirror by TEM _00.
Since the reflection limiting means 18 for limiting the mode is provided, the optical axis can be adjusted more easily than in the case where a diaphragm is provided in the optical path. That is, the position of the mirror is not adjusted according to the position where the optical axis should be (the center line of the diaphragm 14A), but the optical axis is determined in association with the position of the concave mirror 11, so that the optical axis adjustment is not necessary. Strictly speaking, the diffraction loss is also given by the capillary. However, since the diameter of the thin tube is generally sufficiently larger than the diameter of the laser light, the diffraction loss due to the thin tube 14 is extremely small. As a result, even if the positional relationship between the optical axis and the thin tube 14 changes, the change in diffraction loss is small. Therefore, the adjustment of the optical axis can be performed very easily.

Further, even if a force is applied to the glass block 10 to deform it, the position of the laser beam can be changed without being disturbed by the diaphragm 14A as the mirror position is changed. Therefore, the magnitude of the diffraction loss due to the mirror position does not change. Further, since the thin tube 14 is sufficiently wide, the change in diffraction loss due to this is sufficiently small. Therefore, even if the glass block 10 is deformed, the laser output hardly changes.

Further, in the present invention, since the diaphragm 14A does not exist in the optical path, the thin tube 14 formed on the glass block 10
The diameter of can be unified into one type. Also, thin tube 1
Since 4 is sufficiently larger than the diameter of the laser beam, its processing does not require high processing accuracy as compared with the diaphragm 14A.
Therefore, it is possible to obtain advantages such as easier processing than employing the diaphragm 14A, and it is possible to obtain an advantage that a highly reliable ring laser gyro can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of the present invention.

FIG. 2 is a front view for explaining the structure of the main part of the present invention.

FIG. 3 is a characteristic curve diagram for explaining the operation of the main part of the present invention.

FIG. 4 is a plan view for explaining a conventional technique.

[Explanation of symbols]

 10 glass block 11, 12, 13 mirror 14 narrow tube 14A diaphragm 15 ring laser 15A clockwise light 15B counterclockwise light 16A, 16B anode 17 cathode 18 reflection limiting means

Claims (2)

[Claims] 1. A ring laser is formed by rotating a laser beam clockwise and counterclockwise in a closed optical path formed by three or more mirrors, and when the ring laser rotates, the clockwise light and the left beam are rotated. In the ring laser gyro that detects the input angular velocity by utilizing the frequency difference between the surrounding light, in order to limit the transverse mode of laser oscillation to the TEM ₀₀ mode, one or more of the above-mentioned multiple mirrors are used. A ring laser gyro characterized by limiting the area of the reflective surface of the TEM ₀₀ to give diffraction loss to laser light of higher modes than the TEM ₀₀ mode, and suppressing oscillation of laser light of higher modes. 2. The ring laser gyro according to claim 1, wherein one or more reflection surfaces of the plurality of mirrors are provided with reflection limiting means for reducing the reflectance of light in modes other than the TEM ₀₀ mode. A ring laser gyro characterized by.